To meet its customer needs and to differentiate its products and services, AT&T enhances the quality of selected voice calls carried through its inter-exchange network. Once such enhancement currently available is AT&T True Voice.RTM.service, whereby selected frequencies of a voice call are amplified to provide a more pleasing telephone conversation. The manner in which such frequencies are amplified is described and claimed in U.S. Pat. Nos. 5,195,132 and 5, 333,195, both entitled "Telephone Network Speech Signal Enhancement", filed in the name of Duane Bowker et al. and both assigned to AT&T (herein incorporated by reference). Another enhancement available from AT&T is compensation for background noise described in U.S. Pat. Nos. 5,524,148, and 5,485,515, both entitled "Background Noise Compensation in a Telephone Network", filed in the name of Jonathan B. Allen et al. and both assigned to AT&T (herein incorporated by reference). Yet another enhancement provided by AT&T is echo cancellation obtained by routing calls through an echo canceled of a type known in the art.
While the above-described enhancements are useful, they can interact with existing technology, and in some instances, actually impede transmission quality. Presently, calls that require that the enhancement and/or echo cancellation be turned off are routed over separate "overlay" networks. Presently, telecommunications carriers, such as AT&T, use dedicated "overlay" networks to provide specific transmission signal processing, wherein dedicated trunking and tandem switching is implemented to provide specific transmission capabilities. Normally, voice calls are provided echo cancellation and the True Voice.RTM. enhancement, wherein the associated transmission signal processing is provided on trunks denoted as TV on trunks. However, for calls not requiring the TV on signal processing, dedicated overlay networks need to be used. For example, Switched Digital Service (SDS) data-type calls are routed through switching systems within the AT&T's network that turn off the enhancement and echo cancellation. Similarly, those voice and voice band calls requiring echo cancellation but also requiring that the voice enhancement be turned off are typically routed to dedicated via switching systems that provide echo cancellation but have the voice enhancements turned off for both incoming and outgoing trunks. While providing a specialized network to carry calls without enhancement and/or echo cancellation overcomes the problem of undesirable interactions, this approach affords little flexibility in terms of enhancing and/or performing echo cancellation on selected calls within a common network and leads to network capacity inefficiencies because of the need to provide separate dedicated networks for different types of calls, rather than using a single integrated network with a signal processing system (SPS) capability to provide the required transmission processing on a per-call-control (PCC) basis.
Thus, there is a need for a technique for routing calls to enable enhancement and/or echo cancellation of calls on a selected basis.